Should we recommend that relay operators turn on tcp bbr?
The internet seems to have a growing number of howto's for switching your kernel to use the "bbr" congestion control mode of tcp: https://github.com/google/bbr https://en.wikipedia.org/wiki/TCP_congestion_control#TCP_BBR
Thought 1: doing an experiment where various fractions of Tor relays switch to this congestion control mode would be neat. Maybe it's the sort of thing that Shadow could help with, since switching the real Tor network is both cumbersome and dangerous.
(Though, since Shadow builds its own tcp implementation, it would need to have an implementation of the bbr variation in order to do a test with it. And it would need to have realistic non Tor background flows to test the comparison. What a great use case for driving forward Shadow innovation to be able to capture this test. Cc'ing Rob.)
Thought 2: If God wanted us to be using tcp bbr, we'd be using it by default already. And we're not, so we should learn why that is. For example, the wikipedia page indicates that it's not good at fairness in some situations -- and since Tor relays are often guests on their network, we might not want to give people more reasons to get angry at them.